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Date: Wed, 27 Jan 2016 18:31:51 -0800
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao2.yu@...sung.com>
Cc: linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: remove vlist in extent node
Hi Chao,
On Thu, Jan 28, 2016 at 09:36:37AM +0800, Chao Yu wrote:
> Hi Jaegeuk,
>
> > -----Original Message-----
> > From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> > Sent: Thursday, January 28, 2016 5:38 AM
> > To: Chao Yu
> > Cc: linux-f2fs-devel@...ts.sourceforge.net; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH] f2fs: remove vlist in extent node
> >
> > Hi Chao,
> >
> > Hmm. The original patch was just going under testing, and we couldn't post
> > them since there is a kernel panic issue.
> > This patch seems quite better approach, so I think we can integrate both of
> > the patches together.
> >
> > So, how about this patch?
> > Hope you don't mind this.
>
> No objection. :)
Cool. :)
Let me double check your comments below.
Thanks,
>
> >
> > Thanks,
> >
> > From a7844e0438db9ea9d12b7c0c40b655c3371bd6c9 Mon Sep 17 00:00:00 2001
> > From: Hou Pengyang <houpengyang@...wei.com>
> > Date: Tue, 26 Jan 2016 12:56:26 +0000
> > Subject: [PATCH] f2fs: improve shrink performance of extent nodes
> >
> > On the worst case, we need to scan the whole radix tree and every rb-tree to
> > free the victimed extent_nodes when shrinking.
> >
> > Pengyang initially introduced a victim_list to record the victimed extent_nodes,
> > and free these extent_nodes by just scanning a list.
> >
> > Later, Chao Yu enhances the original patch to improve memory footprint by
> > removing victim list.
> >
> > The policy of lru list shrinking becomes:
> > 1) lock lru list's lock
> > 2) trylock extent tree's lock
> > 3) remove extent node from lru list
> > 4) unlock lru list's lock
> > 5) do shrink
> > 6) repeat 1) to 5)
> >
> > Signed-off-by: Hou Pengyang <houpengyang@...wei.com>
> > Signed-off-by: Chao Yu <chao2.yu@...sung.com>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> > fs/f2fs/extent_cache.c | 87 +++++++++++++++++++++-----------------------------
> > fs/f2fs/f2fs.h | 1 +
> > 2 files changed, 37 insertions(+), 51 deletions(-)
> >
> > diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
> > index aae99f2..759b1b1 100644
> > --- a/fs/f2fs/extent_cache.c
> > +++ b/fs/f2fs/extent_cache.c
> > @@ -33,6 +33,7 @@ static struct extent_node *__attach_extent_node(struct f2fs_sb_info *sbi,
> >
> > en->ei = *ei;
> > INIT_LIST_HEAD(&en->list);
> > + en->et = et;
> >
> > rb_link_node(&en->rb_node, parent, p);
> > rb_insert_color(&en->rb_node, &et->root);
> > @@ -63,8 +64,8 @@ static void __release_extent_node(struct f2fs_sb_info *sbi,
> > struct extent_tree *et, struct extent_node *en)
> > {
> > spin_lock(&sbi->extent_lock);
> > - if (!list_empty(&en->list))
> > - list_del_init(&en->list);
> > + f2fs_bug_on(sbi, list_empty(&en->list));
> > + list_del_init(&en->list);
> > spin_unlock(&sbi->extent_lock);
> >
> > __detach_extent_node(sbi, et, en);
> > @@ -147,7 +148,7 @@ static struct extent_node *__init_extent_tree(struct f2fs_sb_info *sbi,
> > }
> >
> > static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
> > - struct extent_tree *et, bool free_all)
> > + struct extent_tree *et)
> > {
> > struct rb_node *node, *next;
> > struct extent_node *en;
> > @@ -157,11 +158,7 @@ static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
> > while (node) {
> > next = rb_next(node);
> > en = rb_entry(node, struct extent_node, rb_node);
> > -
> > - if (free_all)
> > - __release_extent_node(sbi, et, en);
> > - else if (list_empty(&en->list))
> > - __detach_extent_node(sbi, et, en);
> > + __release_extent_node(sbi, et, en);
> > node = next;
> > }
> >
> > @@ -532,7 +529,7 @@ static unsigned int f2fs_update_extent_tree_range(struct inode *inode,
> > }
> >
> > if (is_inode_flag_set(F2FS_I(inode), FI_NO_EXTENT))
> > - __free_extent_tree(sbi, et, true);
> > + __free_extent_tree(sbi, et);
> >
> > write_unlock(&et->lock);
> >
> > @@ -541,14 +538,10 @@ static unsigned int f2fs_update_extent_tree_range(struct inode *inode,
> >
> > unsigned int f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink)
> > {
> > - struct extent_tree *treevec[EXT_TREE_VEC_SIZE];
> > struct extent_tree *et, *next;
> > - struct extent_node *en, *tmp;
> > - unsigned long ino = F2FS_ROOT_INO(sbi);
> > - unsigned int found;
> > + struct extent_node *en;
> > unsigned int node_cnt = 0, tree_cnt = 0;
> > int remained;
> > - bool do_free = false;
> >
> > if (!test_opt(sbi, EXTENT_CACHE))
> > return 0;
> > @@ -561,11 +554,11 @@ unsigned int f2fs_shrink_extent_tree(struct f2fs_sb_info *sbi, int
> > nr_shrink)
> >
> > /* 1. remove unreferenced extent tree */
> > list_for_each_entry_safe(et, next, &sbi->zombie_list, list) {
> > - if (atomic_read(&et->node_cnt)) {
>
> This is used to avoid lock overhead if there are no nodes in the tree.
> Why should we change this?
>
> > - write_lock(&et->lock);
> > - node_cnt += __free_extent_tree(sbi, et, true);
> > - write_unlock(&et->lock);
> > - }
> > + write_lock(&et->lock);
> > + node_cnt += __free_extent_tree(sbi, et);
> > + write_unlock(&et->lock);
> > + if (atomic_read(&et->node_cnt) > 0)
> > + goto unlock_out;
> >
> > list_del_init(&et->list);
> > radix_tree_delete(&sbi->extent_tree_root, et->ino);
> > @@ -587,42 +580,29 @@ free_node:
> > remained = nr_shrink - (node_cnt + tree_cnt);
> >
> > spin_lock(&sbi->extent_lock);
> > - list_for_each_entry_safe(en, tmp, &sbi->extent_list, list) {
> > - if (!remained--)
> > + for (; remained > 0; remained--) {
> > + if (list_empty(&sbi->extent_list))
> > break;
> > - list_del_init(&en->list);
> > - do_free = true;
> > - }
> > - spin_unlock(&sbi->extent_lock);
> > -
> > - if (do_free == false)
> > - goto unlock_out;
> > -
> > - /*
> > - * reset ino for searching victims from beginning of global extent tree.
> > - */
> > - ino = F2FS_ROOT_INO(sbi);
> > -
> > - while ((found = radix_tree_gang_lookup(&sbi->extent_tree_root,
> > - (void **)treevec, ino, EXT_TREE_VEC_SIZE))) {
> > - unsigned i;
> > -
> > - ino = treevec[found - 1]->ino + 1;
> > - for (i = 0; i < found; i++) {
> > - struct extent_tree *et = treevec[i];
> > + en = list_first_entry(&sbi->extent_list,
> > + struct extent_node, list);
> > + et = en->et;
> > + if (!write_trylock(&et->lock)) {
> > + /* refresh this extent node's position in extent list */
> > + list_move_tail(&en->list, &sbi->extent_list);
> > + continue;
> > + }
> >
> > - if (!atomic_read(&et->node_cnt))
> > - continue;
> > + list_del_init(&en->list);
> > + spin_unlock(&sbi->extent_lock);
> >
> > - if (write_trylock(&et->lock)) {
> > - node_cnt += __free_extent_tree(sbi, et, false);
> > - write_unlock(&et->lock);
> > - }
> > + __detach_extent_node(sbi, et, en);
> >
> > - if (node_cnt + tree_cnt >= nr_shrink)
> > - goto unlock_out;
> > - }
> > + write_unlock(&et->lock);
> > + node_cnt++;
> > + spin_lock(&sbi->extent_lock);
> > }
> > + spin_unlock(&sbi->extent_lock);
> > +
> > unlock_out:
> > up_write(&sbi->extent_tree_lock);
> > out:
> > @@ -641,7 +621,7 @@ unsigned int f2fs_destroy_extent_node(struct inode *inode)
> > return 0;
> >
> > write_lock(&et->lock);
> > - node_cnt = __free_extent_tree(sbi, et, true);
> > + node_cnt = __free_extent_tree(sbi, et);
> > write_unlock(&et->lock);
> >
> > return node_cnt;
> > @@ -666,10 +646,15 @@ void f2fs_destroy_extent_tree(struct inode *inode)
> > }
> >
> > /* free all extent info belong to this extent tree */
> > +free_more:
> > node_cnt = f2fs_destroy_extent_node(inode);
> >
> > /* delete extent tree entry in radix tree */
> > down_write(&sbi->extent_tree_lock);
> > + if (atomic_read(&et->node_cnt) > 0) {
> > + up_write(&sbi->extent_tree_lock);
> > + goto free_more;
> > + }
>
> If I understand correctly here, there is no race condition between shrinker
> and destroyer, so it would be safe to usef2fs_bug_on(, et->node_cnt)?
>
> Thanks,
>
> > f2fs_bug_on(sbi, atomic_read(&et->node_cnt));
> > radix_tree_delete(&sbi->extent_tree_root, inode->i_ino);
> > kmem_cache_free(extent_tree_slab, et);
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index c4e723b..4e7eab9 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -354,6 +354,7 @@ struct extent_node {
> > struct rb_node rb_node; /* rb node located in rb-tree */
> > struct list_head list; /* node in global extent list of sbi */
> > struct extent_info ei; /* extent info */
> > + struct extent_tree *et; /* extent tree pointer */
> > };
> >
> > struct extent_tree {
> > --
> > 2.6.3
>
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